This application is to assess the behavioral predictors of weight maintenance and weight loss maintenance among young adults in the Growing Up Today Study (GUTS) and middle-aged women in the Nurses'Health Study II (NHS II). Few people are able to maintain their weight, most gain weight during young adulthood and middle age. Moreover, many people attempt to lose weight, but few people who lose weight are able to maintain their loss(es). Little is known about weight loss maintenance among young adults. The dramatic increase in the prevalence of overweight and obesity over the past two decades highlights the need for the identification of factors that promote weight maintenance instead of weight gain. Although some dietary, behavioral, and pharmacotherapy regimes have been observed to promote weight loss, it is unknown which strategies promote the long-term maintenance of weight and whether the same factors are helpful for weight maintenance and weight loss maintenance. We will analyze data from the 10688 individuals in GUTS who at least 16 years of age and 64,492 non-pregnant middle-aged women in the NHS II. We will assess whether frequent exercise predicts being able to maintain weight, whereas, using dietary strategies without exercise is insufficient to maintain weight intentionally lost. We will determine if the use of diet pills, fasting, and crashing dieting decrease the likelihood of maintaining weight and whether using behavioral approaches, .. such as limited portion sizes, increases the likelihood of maintaining weight lost intentionally. We will assess the magnitude of these associations and whether they vary by age group or weight status (i.e., underweight, healthy weight, overweight, or obese). Since the GUTS participants are offspring of women in the NHS II, in secondary analyses we will assess whether the weight control practices and weight changes of mothers and their daughters are associated. This study will have good power to detect moderate associations (e.g., relative risk >= 1.4 or <= 0.6). Overweight and obesity are serious public health problems in the United States, therefore identifying predictors of successful weight maintenance and weight loss maintenance is of considerable importance. Most of the research has been conducted among adults, many of whom have been struggling with their weight for decades, thus studying both young adults and middle-aged women will provide important information that is needed by many Americans.